We hypothesize that we will be able to identify genes contributing to hypertension in African Americans by focusing on the physiological pathways that determine arterial pressure. Over the past 6 years, we have extensively characterized African Americans for phenotypes related to cardiovascular and renal function. Based on recently completed genome scans, we have identified several chromosomal regions likely to contain genes influencing hypertension-related phenotypes in hypertensive, African American sib pairs. For several phenotypes, overlapping QTLs have also been identified in related studies in a genetically isolated French Canadian population and/or in homologous chromosomal regions in the F2 cross of Dahl-salt sensitive x normotensive Brown Norway rats. We now propose to extensively phenotype 500 hypertensive and 500 normotensive African American subjects to conduct a genetic association study, using a SNP genomic scan approach. To achieve a clear separation of blood pressures from hypertensive subjects, normotensive subjects will be selected from the lower third of the population-based blood pressure distribution. Hypertensive (BMI), and age. Inclusion of phenotypes is based on their relevance to the pathophysiology of hypertension and prior evidence of "heritability." Candidate genes for SNP analysis will be selected within chromosomal regions of two QTLs that we have previously demonstrated to be linked to hypertension-related phenotypes--a QTL for body mass index on chromosome 1 and a QTL for microalbuminuria on chromosome 18. SNP analyses will be carried out in 15 percent of the genes within each of these QTLs, and genes will be selected on the basis of their relevance to hypertension, including documented sequence conservation for blood pressure related QTLs with rat or mouse. The final goal of the project is to determine if distinct clusters of blood pressure related phenotypes can be identified that will permit stratification of hypertensive individuals into distinct subgroups to facilitate the analysis of the genetic determinants of hypertension and/or provide mechanistic leads to genes contributing to these traits.